LIFE HISTORY OF LAKE HERRING OF LAKE HURON 397 



from the total lengths of Table 43. (For the individual average length increments 

 of each year of these fish see Table 39.) By this method of combination more than 

 one age group is involved in most of the averages of the calculated increments. To 

 each younger year class, beginning with that of 1917, ayounger age group is added in 

 the table. Obviously the progressive increase in the averages of the first year of life 

 after 1918, as shown in Table 61, may be due in part to Lee's "phenomenon" and 

 not entirely to an acceleration in growth rate. However, the values for the year 

 classes older than 1917 may involve Lee's "phenomenon" also, so in this respect the 

 two series of averages are comparable. Even so, we are not attempting to compare 

 here the corresponding averages of each year class separately. As was the case in 

 Table 60, the averages of the herring taken in 1917 are based on too few specimens 

 to be accurate, but here again their significance lies partly in the consistency of the 

 results based on them. We point out merely that the increment averages for the 

 calendar years preceding 1915 and succeeding 1918 are greater, on the whole, than 

 those for the years 1915 to 1918. Whether or not the progressive increase in the 

 growth rate of the 1-year fish after 1918 is due partly to Lee's "phenomenon" seems 

 to me to be immaterial in the present discussion. That the fish actually grew faster 

 subsequent to 1918 than during the period 1915 to 1918 has been shown in the dis- 

 cussion of Tables 35 to 39 (pp. 363 to 369). It is to be noted that for some years two 

 averages that are widely divergent are given for fish of the same year class. In such 

 case that average based on the larger number of specimens presumably is the more 

 accurate and is so considered throughout this discussion. 



An examination of the growth rates of the first year of life, as given in Table 61, 

 shows that those of the years 1911 to 1914, inclusive, were higher in general than 

 those of the years 1915 to 1918, inclusive, and as high as those of the years 1919 to 

 1922, inclusive. The growth rates of the second year of life of the years 1914 and 

 1915 exceeded those of the years 1916 to 1918, inclusive, but were less than those of 

 the years following 1918; those of the years 1912 and 1913 were about the same as 

 those given for the period 1916 to 1918. The rates of growth of the third year of life 

 of the years 1914 and 1915 exceeded those of any succeeding years, while those of the 

 years 1913 and 1916 were about the same as those of the years 1917 and 1918. The 

 data suggest that 1913 was an unfavorable year for the growth of the herring consid- 

 ered, and that 1915 was unfavorable for the growth of the 1-year herring but favor- 

 able for that of herring of years II and III. If the latter statement be true, our pre- 

 vious statements that the period of low growth rates included the years 1915 to 1918 

 must be modified somewhat, as follows: Low growth rates prevailed among the her- 

 ring of year I during the period 1915 to 1918, and among those of years II and III dur- 

 ing the period 1916 to 1918. It appears valid to conclude now that the data of Tables 

 60 and 61 indicate that the low growth rates prevailing among the herring of Sagi- 

 naw Bay during the period 1915 (1916) to 1918 were abnormal; that, in general, 

 higher rates prevailed before 1915 (1916) and were resumed in 1919. Apparently, 

 then, the growth rates prevailing among the herring in Saginaw Bay before 1915 

 (1916) were in some way inhibited during the period 1915 (1916) to 1918 and restored 

 or partly restored in 1919. Growth conditions in the bay were unfavorable during 

 the years 1915 (1916) to 1918, inclusive. 



